Medical conditions associated with irregular blood flow to the extremities of a subject, including peripheral arterial disease (“PAD”), diabetic foot ulcers, and critical limb ischemia (“CLI”), are diagnosed using a number of invasive and non-invasive procedures. These procedures include ankle-brachial index (ABI) measurement, plethysmography, transcutaneous oxygen tension (TcPo2) measurements Doppler and ultrasound imaging, computed tomographic angiography (CT), magnetic resonance angiography (MRA), angiography. Each of these procedures, however, provides incomplete information on the underlying condition.
ABI, for example, provides an indication of narrowing or blockage of arteries supplying a subject's legs by measuring differences between a patient's blood pressure at their arms and ankles. However, the procedure does not measure the oxygenation level of the blood flowing to the extremities, the distribution of oxygen at an affected tissue, or the efficiency of oxygen delivery to the tissue. Similarly, plethysmography, Doppler, ultrasound imaging, CT imaging, and MRA imaging provide an indication of the arterial capacity or actual blood flow at the extremities, without providing information on the oxygenation level of the blood flowing to the extremities, the distribution of oxygen at the affected tissue, or the efficiency of oxygen delivery to the tissue. TcPo2, on the other hand, measures the level of oxygenation at a single point below the skin, but does not measure global blood flow, distribution of oxygen at an affected tissue, or the efficiency of oxygen delivery to the tissue.
As such, these techniques provide a medical professional with incomplete information for diagnosing and treating conditions associated with irregular blood flow or lack of adequate oxygen delivery to an affected site. However, use of these techniques is propagated by medical reimbursement schemes that set a fixed or capped reimbursement for studies of peripheral arterial function, because of the relative inexpensive nature of these tests, with respect to the costs associated with the medical professional's time, measurement equipment, and incidental expenses. For example, the American Medical Association established a set of codes—the Current Procedural Terminology (“CPT”) codes—that classify treatment for medical and surgical procedures, diagnostic tests, laboratory studies, and other medical services rendered to subjects. The codes provide a uniform system for detailing medical, surgical, and diagnostic services provided by a medical professional, to communicate services rendered to third-parties reimbursing the services, e.g., insurers.
The CPT codes associated with peripheral arterial studies include: CPT 93922, used to report noninvasive single level, bilateral physiologic studies of upper or lower extremity arteries; CPT 93923, used to report noninvasive multiple level, complete bilateral physiologic studies of upper or lower extremity arteries; and CPT 93924, used to report noninvasive physiologic studies of lower extremity arteries, at rest following treadmill stress testing. The average reimbursements associated with Current Procedural Terminology (“CPT”) codes 93922, 93923, and 93924, however, ranges between only $120 (CPT 93922) and $220 (CPT 93924). This does not provide a medical establishment with much, if any, room or incentive to implement technological advances into the medical exam, constraining medical professionals to use of traditional—but ill-suited methods—for diagnosing conditions associated with irregular blood flow to the extremities.
Hyperspectral (also known as “multispectral”) spectroscopy is an imaging technique that integrates multiples images of an object resolved at different spectral bands (i.e., ranges of wavelengths) into a single data structure, referred to as a three-dimensional hyperspectral data cube. Data provided by hyperspectral spectroscopy is often used to identify a number of individual components of a complex composition through the recognition of spectral signatures of the individual components of a particular hyperspectral data cube. As such, hyperspectral imaging is a more appropriate tool for diagnosis and prognosis of medical conditions associated with irregular blood flow to the extremities of a subject because of its capability to provide information related to blood flow, oxygenation levels of blood delivered to the extremities, distribution of oxygen at an affected tissue, and efficiency of oxygen delivery to the tissue.
Despite the great potential clinical value of hyperspectral imaging, several drawbacks have limited the use of hyperspectral imaging in the clinic setting. In particular, current medical hyperspectral instruments are costly because of the complex optics and computational requirements currently used to resolve images at a plurality of spectral bands to generate a suitable hyperspectral data cube. Hyperspectral imaging instruments can also suffer from poor temporal and spatial resolution, as well as low optical throughput, due to the complex optics and taxing computational requirements needed for assembling, processing, and analyzing data into a hyperspectral data cube suitable for medical use. Moreover, because hyperspectral imaging is time consuming and requires complex optical equipment, it is more expensive than the conventional methods. Thus, medical establishments could not afford to employ such technology because of the relatively small reimbursements available for peripheral arterial studies.
Thus, there is an unmet need in the field for methods of fulfilling the requirements for reimbursement under a current procedural terminology code associated with an extremity arterial study of a subject, while providing high power diagnostic and prognostic medical information.